This invention relates to gas chromatography. More particularly, it relates to an arrangement of a sampling valve and a backflush valve which are capable of being operated independently of one another as well as relating to two temperature control zones, all of which cooperate with a single chromatographic column and a detector means to provide the capability for very accurate, rapid, on-line analysis of process streams, particularly organic process streams containing trace amounts of water and chlorine or hydrogen chloride.
In general, gas chromatography is an analytical technique widely used for the qualitative and quantitative analysis of liquid and gaseous mixtures. In recent years this technique has become increasingly important in determining components present in a sample to be analyzed. In general, a sample of a mixture is obtained from a stream to be analyzed and passed through one or more columns wherein the components are separated and then separately passed to a detector which measures the separated components of the mixture in order of their elution times. Columns may be then backflushed to remove any retained components from the column.
It is known to provide means such as a sampling valve wherein a small sample of a liquid or a gaseous mixture is measured and then carried into the column by means of a carrier gas, in which column the components of the mixture are separated and gradually eluted from the column into the detector means. In the chromatographic analysis of a sample containing both easily and difficultly eluted components, the more rapidly eluted component is separated and passed into the detector well before the more difficultly eluted component leaves the chromatographic column. When this type of analysis is being run, it is known practice to backflush the chromatographic column with a stream of carrier gas or a suitable flushing gas to remove the retained components through the inlet end of the chromatographic column. Backflushing of this type frees the column for another analysis. Suitable valving and lines must be supplied in addition to the basic apparatus to permit this backflushing.
In many chromatographic analyses two or more chromatographic columns are connected in series. It is also known to provide one or more valves programming the several carrier and backflushing gas streams as well as sample streams to efficiently operate the chromatographic analysis. Such arrangements as are presently known, involving several columns and/or several valves, are time consuming and add to the equipment and maintenance costs.
It is further known to use a single programming valve which performs simultaneous sampling and backflushing in a gas chromatographic system containing a single chromatographic column and detector; said column and detector being connected directly together to avoid dead space between them. See Jones, A. W., "Multi-Stream Gas Chromatographic Method and Apparatus", U.S. Pat. No. 3,916,465, issued Nov. 4, 1975.
There are many things known about making gas chromatographic analyzers. Nevertheless maintaining the accuracy of gas chromatographic devices, while making them sufficiently reliable to be placed in on-line process stream monitoring duty has not been achieved while also giving them the ability to immediately switch into a backflush mode once the component of the stream being monitored is detected and further giving such device sufficient flexibility to be adjusted for different stream component analysis, that is adjusted as to time of sample injection at time and length of backflushing.
It would be advantageous to have a gas chromatographic analyzer and method which is simple yet which is capable of rapid, repetitive gas chromatographic analysis of process streams with greater accuracy, durability, and flexibility than heretofore available. These advantages are found in the present invention.